Connect the dots: 1) Heard about a new (small) eruption of Piton de la Fournaise. 2) Piton de la Fournaise is the current "expression" of the La Reunion mantle plume. 3) Thought about what happened when the Indian subcontinent passed over the La Reunion plume = Deccan Traps volcanism. 4) Tried to find a good picture of the Deccan Traps. 5) Discovered that one of the few places to see Deccan Trap basalt layering is Lonar Crater. 6) Lonar Crater is said to be the only impact crater on volcanic basalt. 7) Found remote sensing and surface pictures of Lonar Crater and posted them here. 8) See below for the ironic part.

Ironic part: For years, I've been reading and following the ongoing dispute regarding the ultimate cause of the extinction of the dinosaurs. It seems that there is a slowly emerging consensus that it happened because of the somewhat simultaneous occurrence of two events: the Deccan Trap volcanism and the Chicxulub (Yucatan) asteroid impact. As best can be dated, the Deccan Trap volcanism occurred in the 1 million years preceding the Chicxulub impact, and the gases from the volcanism caused climate changes that made it tough to live -- and Chicxulub made it much more difficult.

The ironic part is that Lonar Crater is an impact on the Deccan Trap volcanism, but is a very recent impact.

I can explain. The controversy regards the cause of the extinction of the dinosaurs. For a long time, the main idea was climate change near the end of the Cretaceous, basically a slow process. The Alvarez team determined that the K/T boundary (Cretaceous/Tertiary -- I've never known why K was the Cretaceous letter) had an iridium anomaly most likely caused by an asteroid impact, so they suggested that an asteroid impact wiped out the dinos. This was initially viewed as crackpot, slowly gained credibility, and took the lead when the big Chicxulub impact structure on the Yucatan was identified as being just the right age. But there are problems with the theory -- mainly that not everything died out right then, and though catastrophic, an impact is so short-lived that it doesn't seem that it could accomplish full extinctions. So it's been noted that the Deccan Trap flood basalt period -- when the Indian subcontinent passed over the "plume" of volcanic activity currently located on the island of Reunion, east of Madagascar -- took place for about 1 million years just before the Chicxulub impact. Flood basalts are huge outpourings of lava, accompanied by large releases of volcanic gas.

Put the two together, and it appears there was a million-year long period of altered climate caused by volcanic activity, finishing with a powerful impact that could have pushed a lot of species with tenuous holds on existence over the edge to extinction.

This crater is a recent impact on the Deccan Trap flood basalts, so it superimposes the two active factors that appear to have caused the end of the dinosaurs and which mark the end of the Cretaceous period.

Thanks. That's about the time of the Barringer crater in Arizona. I wonder if we recieved a swarm at that time.

Or just statistical variability. But I'm not belittling the idea -- it seems to me that there are a number of craters (Manicougan in Quebec being one) that are dated to a very similar time period. Searching...

This is believed to have contributed to the end-of-the-Triassic extinction event. This is not certain, however (it's not certain that the five impacts cited in the article all happened at the same time, but they were "geologically" close).

regarding the erosion, the plain is probably really hard basalt, so erosion would take a while. The various bits of crap that lay there as a consequence of the disintegration of the impactor (and the rock that had been where the crater is now) washed away long ago, no doubt.

A team of scientists working on two continents has discovered that a series of five craters on Europe and North America form a chain, indicating the breakup and subsequent impact of a comet or asteroid that collided with Earth approximately 214 million years ago.

The impacts may have contributed to a mass extinction that occurred at the end of the Triassic periodone of the five greatest mass extinctions in history.

The work, by scientists at the University of Chicago, the University of New Brunswick (Canada) and The Open University (Milton Keynes, U.K.) is published in a paper in the Thursday, March 12, issue of the journal Nature.

When scientists observed the impacts of the pieces of Comet Shoemaker-Levy 9 on Jupiter in July 1994, they said that the impact of a fragmented comet could never happen here on Earth because the Earths gravitational field is too weak to break a comet into pieces, said David Rowley, University of Chicago Associate Professor in Geophysical Sciences. But our studies of these five craters provide compelling evidence that this happened at least once, and theres no reason it couldnt have happened more than that.

Rowleys colleagues, John Spray, a structural geologist from the University of New Brunswick, and Simon Kelley from The Open University, were interested in the relationship between impact craters of similar ages. Kelley had developed a technique to date such craters more preciselyusing laser argon/argon dating of the glass formed by localized heating of the rock. They asked Rowley to help figure out how the craters were aligned when the impacts occurredbecause of plate tectonics, the continents have moved extensively in the last 214 million years.

Rowley, a principal investigator for the University of Chicagos Paleogeographic Atlas Project, which is compiling an atlas of the paleogeography and paleoclimate of the world as it changed over the past 500 million years, had that kind of information at his fingertips.

I get these kinds of requests all the time, said Rowley, so at first I didnt think about it too much. But when they asked to me take a closer look at the data and I saw the alignment, I just said, wow!

Three of the five craters, Rochechouart in France, and Manicouagan and Saint Martin in Canada, were at the same latitude22.8 degreesforming a nearly 5000-kilometer chain. The other two, Obolon in Ukraine and Red Wing in Minnesota, lay on identical declination paths with Rochechouart and Saint Martin, respectively. All of the craters are previously known and well-studied, but the paleoalignment has never before been shown.

One possible explanation for the alignments of the five craters is a fragmented comet that crashed to Earth in three major groups over a period of time as short as four hours, in two groups of two and one solitary chunk. It is possible that the comet or asteroid actually broke into more than five pieces, but most of the Earth at that latitude was ocean 214 million years ago, and evidence of any ocean-bottom craters has long been obliterated. The impacts may have occurred over a period of several days, depending on how widely the fragments were dispersed.

Rowley said that the chance that these craters are randomly aligned is near zero.

Manicouagan, the largest of the five craters, is more than 100 kilometers in diameter, comparable to the 170-kilometer Chixulub crater in the Yucatanthe impact that is believed to have caused the mass extinction at the end of the Cretaceous period 65 million years ago, killing the dinosaurs.

The Triassic extinction was equivalent in magnitude to the Cretacious/Tertiary (K/T) extinction: about 80% of the species then living on the planet became extinct.

There are 150 known impact craters worldwide; the group is now studying others to see if there are other coincident crater chains.

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